When integrated circuits communicate with each other via printed-circuit boards at high data rates, the signals may suffer channel-induced distortion including frequency-dependent attenuation. Where the signals represent a sequence of data symbols, e.g., logic-high values and logic-low values, encoded as voltage levels, the distortion can smear symbol representations so that they overlap, resulting in inter-symbol interference (ISI).
Channel-induced distortion can be addressed using transmitter pre-emphasis and receiver equalization. Transmitter pre-emphasis typically involves selecting settings for a “finite impulse response” (FIR) filter, while receiver equalization involves selecting settings for an analog high-pass filter. Various transmitter pre-emphasis and receiver equalization settings can be evaluated by measuring a bit-error rate (BER) for the receiver output data. For example, receiver initialization can involve sweeping equalizer settings, inputting a training pattern at each equalizer setting, measuring a receiver-data BER by comparing the receiver output data with the training pattern, and selecting a setting with a minimum BER for the receiver output data.